isConst - help

[sks_cpp]

How can I get the following to work? Are the templates defined incorrectly?
I am running this on Visual C++ 6.0.


// =============== =============== =============== ==

#include <iostream>
using namespace std;

namespace utl
{
template <typename T>
class TypeTraits
{
private:
template<class U>
struct UnConst
{
typedef U Result;
enum { isConst = false };
};

template<class U>
struct UnConst<const U>
{
typedef U Result;
enum { isConst = true };
};

struct UnConst<class U*>
{
typedef U Result;
enum { isConst = false };
};

struct UnConst<class U* const>
{
typedef U Result;
enum { isConst = true };
};


struct UnConst<class U const *>
{
typedef U Result;
enum { isConst = true };
};

public:

enum { isConst = UnConst<T>::isC onst };
};
}

class Object
{
public:
Object(int a) { i = a; }
int i;
};

int main()
{
Object test(10);
const Object* t = &test;

if ( utl::TypeTraits <Object* const>::isConst )
cout << "Hooray - it's a const :)\n";
else if ( utl::TypeTraits <Object const *>::isConst )
cout << "Hooray - it's a const :)\n";
else if ( utl::TypeTraits <const Object *>::isConst )
cout << "Hooray - it's a const :)\n";
else if ( utl::TypeTraits <Object const>::isConst )
cout << "Hooray - it's a const :)\n";
else if ( utl::TypeTraits <const Object>::isCons t )
cout << "Hooray - it's a const :)\n";
else
cout << "It's NOT a const :(\n";


if ( utl::TypeTraits <Object*>::isCo nst )
cout << "it's a const :(\n";
else
cout << "Hooray - It's NOT a const :)\n";

cout << endl;

return 0;
}
// =============== =============== ===============

// Output

It's NOT a const :(
Hooray - It's NOT a const :)

[tom_usenet]

Re: isConst - help

On Thu, 24 Jul 2003 12:06:20 GMT, "sks_cpp" <sksjava@hotmai l.com>
wrote:
[color=blue]
>How can I get the following to work? Are the templates defined incorrectly?
>I am running this on Visual C++ 6.0.[/color]

Visual C++ 6 doesn't have partial template specialization, so you are
out of luck. You need to upgrade to VC++ 7.1
[color=blue]
>
>// =============== =============== =============== ==
>
>#include <iostream>
>using namespace std;
>
>namespace utl
>{
> template <typename T>
> class TypeTraits
> {
> private:
> template<class U>
> struct UnConst
> {
> typedef U Result;
> enum { isConst = false };
> };
>
> template<class U>
> struct UnConst<const U>
> {
> typedef U Result;
> enum { isConst = true };
> };[/color]

Ok so far. But I'm not sure why you have the following (incorrectly
written) specializations . They aren't needed.
[color=blue]
>
> struct UnConst<class U*>[/color]

Should be:

template <class U>
struct UnConst<U*>
[color=blue]
> {
> typedef U Result;
> enum { isConst = false };
> };
>
> struct UnConst<class U* const>[/color]

Should be:
template <class U>
struct UnConst<U* const>

[color=blue]
> {
> typedef U Result;
> enum { isConst = true };
> };
>
>
> struct UnConst<class U const *>[/color]

Again.
[color=blue]
> {
> typedef U Result;
> enum { isConst = true };
> };
>
> public:
>
> enum { isConst = UnConst<T>::isC onst };
> };
>}
>
>class Object
>{
>public:
> Object(int a) { i = a; }
> int i;
>};
>
>int main()
>{
> Object test(10);
> const Object* t = &test;
>
> if ( utl::TypeTraits <Object* const>::isConst )
> cout << "Hooray - it's a const :)\n";
> else if ( utl::TypeTraits <Object const *>::isConst )[/color]

That isn't a const, by my reckoning.
[color=blue]
> cout << "Hooray - it's a const :)\n";
> else if ( utl::TypeTraits <const Object *>::isConst )
> cout << "Hooray - it's a const :)\n";
> else if ( utl::TypeTraits <Object const>::isConst )
> cout << "Hooray - it's a const :)\n";
> else if ( utl::TypeTraits <const Object>::isCons t )
> cout << "Hooray - it's a const :)\n";
> else
> cout << "It's NOT a const :(\n";
>
>
> if ( utl::TypeTraits <Object*>::isCo nst )
> cout << "it's a const :(\n";
> else
> cout << "Hooray - It's NOT a const :)\n";
>
> cout << endl;
>
> return 0;
>}
>// =============== =============== ===============
>
>// Output
>
>It's NOT a const :(
>Hooray - It's NOT a const :)[/color]

Take a look at boost's type traits. www.boost.org. They don't work
(properly) on VC6 though - it is 5 years old now so it isn't
surprising!

Tom